I believe this is a bug in Jekyll, specifically Issue #2334, which looks like it's been fixed within the last 24 hours, but may not have made it out into the gem distribution yet.
Given that Jekyll 2 has only just been released, it might be a good idea to check the issues log in the GitHub project first if you find anything that feels buggy. (Github's top search bar will search the issues for a repository as well as the code.)
As Sylvain notes in his answer, this has now been corrected in Jekyll 2.0.3, so an update should fix things for you.